Sesamoids and Accessory Bones of the Foot

Location, Function, and Size

The sesamoid mechanism and intrinsic musculature of the hallux differentiate the first ray from the lateral toes. The hallucal sesamoids, enveloped within the double tendon of the flexor hallucis brevis ( Fig. 11-1 ), articulate on their dorsal surface with the plantar facets of the first metatarsal head. A crista, or intersesamoid ridge ( Fig. 11-2 ), separates the medial and lateral metatarsal facets. This intersesamoid ridge provides intrinsic stability to the sesamoid complex. In a hallux without abnormalities, the entirety of the sesamoid will sit medial or lateral to the intersesamoid ridge. In severe cases of hallux valgus, with substantial subluxation of the sesamoid complex in relation to the first metatarsal head, the intersesamoid ridge atrophies and at times is obliterated ( Fig. 11-3 ). Close inspection of the plantar articular surface of the first metatarsal frequently reveals substantial cartilage erosion and degenerative arthritis in this area ( Fig. 11-4 ).

The sesamoids are connected to the plantar base of the proximal phalanx through the plantar plate ( Fig. 11-5 ), which is an extension of the flexor hallucis brevis tendon. The inferior surface is covered by a thin layer of the flexor hallucis brevis tendon, whereas the superior surface is articular in nature. These hallux sesamoids are entirely intratendinous, except dorsally, where they articulate with the first metatarsal head. They are suspended by a sling-like mechanism composed of the collateral ligaments of the MTP joint and the sesamoid ligaments ( Fig. 11-6 ) on both the medial and lateral aspects of the MTP joint. The flexor hallucis brevis, through its sesamoid mechanism, provides a significant plantar flexion force at the MTP joint. The sesamoids also have an insertion into the joint capsule and the plantar aponeurosis; this provides both stabilization and a static plantar flexion force at the MTP joint.

On the medial aspect of the MTP joint, the abductor hallucis tendon ( Fig. 11-7 ) inserts into the plantar-medial base of the proximal phalanx as well as the medial sesamoid and functions to stabilize the sesamoid mechanism medially. On the lateral aspect, the adductor hallucis tendon inserts into the lateral base of the proximal phalanx and into the lateral sesamoid to stabilize the sesamoid mechanism laterally. The medial and lateral sesamoids are connected by the intersesamoidal ligament, which forms the base of the tendinous canal enveloping the tendon of the flexor hallucis longus.

Distal to the sesamoids, a number of structures coalesce to form the plantar plate. These include the phalangeal-sesamoid ligament, a thin-layered structure that interdigitates with the collateral ligaments, extension of the plantar aponeurosis, and tendons of the flexor hallucis brevis. Complete or partial rupture of the plantar plate attachment may lead to a turf toe deformity with retraction of the sesamoids, restricted motion, and degenerative arthritis of the first MTP joint.

When a person is in a standing position, the sesamoids are located posterior to the metatarsal head; however, with dorsiflexion of the hallux, the sesamoids move distally, thereby protecting the otherwise exposed plantar surface of the first metatarsal head. When a person rises onto the toes, the sesamoids (especially the medial sesamoid) act as the main weight-bearing focus for the medial forefoot ( Fig. 11-8 ).

Kewenter noted that the medial sesamoid is located slightly more distal than the lateral sesamoid and is slightly larger. Orr quantitated sesamoid size and reported that the tibial sesamoid averaged 9 to 11 mm in width and 12 to 15 mm in length. The fibular sesamoid was noted to have an average width of 7 to 9 mm and an average length of 9 to 10 mm.

Ossification

Although ossification of the hallucial sesamoids is variable, Kewenter reported that ossification usually occurs between the sixth and seventh years. Ossification of the sesamoids often occurs from multiple centers, and this may be the reason for the development of multipartite sesamoids.

Circulation

The arterial anatomy of the first ray was evaluated in 22 anatomic specimens by Rath et al. They found that the first plantar metatarsal artery provided the main arterial supply to the medial and lateral sesamoids. It anastomosed with a branch of the medial plantar artery in 90% of cases, and both proximal and distal vessels branch off the two major arteries. Pretterklieber and Wanivenhaus, in dissections of 29 cadavers, reported three different types of arterial circulation. The most common type (type A, 52%) was characterized by arterial circulation derived from the medial plantar artery and the plantar arch. In the less common types, circulation was derived mainly from either the plantar arch or only from the medial plantar artery ( Fig. 11-9 ).

The course and distribution of the arterial circulation to the sesamoids might have a bearing on the development of avascular necrosis after trauma or inadvertent injury during surgical exploration of this area. The number of arterial branches can affect healing of fractures as well as the incidence of avascular necrosis after trauma. Multiple arterial branches can protect an injured sesamoid, whereas a single arterial branch to a damaged sesamoid may be interrupted by a fracture or injury and lead to delayed healing or a nonunion.

Sobel et al and Rath et al mapped the vascular supply of both the medial and lateral sesamoids. The major vascular supply enters the sesamoids from the proximal and plantar aspect, with a minor arterial supply entering through the distal pole of the sesamoids ( Fig. 11-10A ). The distal vascular supply originates through distal capsular attachments providing, in most cases, a limited arterial supply. The proximal arterial supply, through the flexor hallucis brevis, supplies one third to two thirds of the proximal sesamoid. Vascular anastomoses occur between the proximal supply and that derived from the plantar surface to the body of the sesamoid ( Fig. 11-10B ). The distal portion of the sesamoid has the most tenuous vascular supply, and this can lead to delayed or unsuccessful healing after injury.

The sesamoids not only absorb weight-bearing forces on the medial aspect of the forefoot but also increase the mechanical advantage of the intrinsic musculature in plantar-flexing the proximal phalanx. The tendon of the flexor hallucis longus is protected in its tendon sheath by the medial and lateral sesamoids and provides a plantar flexion force to the distal phalanx of the great toe.

Bipartite Sesamoids and Fractures

The incidence of partite sesamoids as well as their cause has been the subject of substantial discussion in the literature ( Table 11-1 ). They most frequently involve a singular sesamoid, being the tibial sesamoid in 87% to 96% of bipartite sesamoids ( Fig. 11-11 ). However, they may also involve both sesamoids of the same hallux. Dobas and Silvers found a 19% incidence of combined tibial and fibular sesamoid bipartism ( Fig. 11-12 ). The medial sesamoid is often divided into two, three, or four parts, whereas the lateral sesamoid is rarely divided into more than two parts ( Fig. 11-13 ).

While initially bilaterally was considered very common, larger studies showed the rate of bilaterally to be much lower. Rowe noted 90% of bipartite sesamoids were bilateral, and Giannestras stated that the occurrence of bipartite sesamoids was typically symmetric. However, Dobas and Silvers found that only 25% of partite tibial sesamoids had an identical bipartite tibial sesamoid on the contralateral side. Jahss noted that bipartism was 10 times more common in the medial sesamoid.

Inge and Ferguson reported that 85% of the bilateral partite sesamoids had asymmetric divisions. They also reported that the incidence of division decreased with time, thus implying that osseous union occurs with time in the divided sesamoid. They further reported that histologic evaluation of congenital bipartite sesamoids demonstrated that articular cartilage tended to dip down between the two osseous fragments. This can predispose a bipartite sesamoid to fracture or disruption of the synchondrosis with minimal injury (see Fig. 11-11D ). They speculated that the medial sesamoid has a higher frequency of bipartism than the lateral sesamoid because it is more often traumatized, a result of its greater weight-bearing capacity. It has not been determined whether continued trauma with ambulation prevents the union of divided sesamoids or whether some of these partite sesamoids are actually nonunions of fractures.

The incidence of irregular ossification with bipartism in the medial sesamoid is well recognized. Kewenter examined a series of sesamoids in cadavers and found that congenitally divided sesamoids fracture with much less force than normal sesamoids when experimental trauma was introduced. Although fractures of sesamoids are relatively rare, numerous cases have been reported in the literature. Substantial trauma with MTP joint dislocation and simultaneous fractures of both sesamoids have been reported ; in general, the most frequently reported mechanism of injury is a fall onto the forefoot, sudden loading of the forefoot, or a crush injury.

It can be difficult to distinguish between a fractured sesamoid (see Fig. 11-13 ) and a symptomatic bipartite sesamoid. With a divisionary line between two segments of a sesamoid, a careful physical examination and history must be correlated with radiographic findings to differentiate between a partite sesamoid and a superimposed fracture. With a sesamoid fracture, pain is localized to the region of the specific sesamoid. Symptoms are typically exacerbated with ambulation and reduced with rest. Often, the patient ambulates with weight bearing on the lateral aspect of the foot to avoid motion and loading of the sesamoid complex.

On physical examination, forced passive dorsiflexion and plantar flexion can cause discomfort. Synovitis or nonspecific swelling on the plantar aspect of the sesamoid complex may be observed. The development of pain after minimal trauma in the presence of a bipartite sesamoid should alert the examiner to the possibility of a superimposed fracture of a bipartite sesamoid.

An acute fracture may be noted on a radiograph with a sharp radiolucent line ( Fig. 11-14 ). An MRI can confirm the diagnosis demonstrating the fracture line and edema at the sesamoid (see Fig. 11-14E and F ). However, Inge and Ferguson suggested that a fracture should not be diagnosed unless bony callus is present. Delay in diagnosis of a sesamoid fracture is therefore common because of the difficulty of confirming the fracture by radiography. Although rarely is a preinjury film available to help differentiate a partite sesamoid and a fracture, increased separation between fragments can be a definitive finding in the presence of a disruption of a partite sesamoid ( Fig. 11-15 ). Richardson recommends a bone scan to aid in diagnosis of a fracture in the presence of a bipartite sesamoid. MRIs may demonstrate increased vascularity, bone edema, or acute changes, indicating a disruption of a partite sesamoid (see Fig. 11-35D ).

Treatment

Custom and prefabricated orthotics and scaphoid and metatarsal pads can relieve pressure in the sesamoid region, diminishing symptoms. Taping of the toe to reduce dorsiflexion can also relieve symptoms. Rosenfield and Trepman have described the use of a rocker-soled walking shoe with a full-length steel shank. An orthotic insole is added with a recess beneath the sesamoid region ( Fig. 11-16 ). Hobart recommended non–weight bearing and casting an acute sesamoid fracture had healed, which usually occurred in 6 to 8 weeks ( Fig. 11-17 ).

If conservative methods fail, surgical treatment of the involved sesamoid may be necessary ( Fig. 11-18 ). A meta-analysis comparing nonoperative versus surgical treatment of sesamoid fractures demonstrated an earlier return to sports by 2.9 weeks with operative treatment. Moreover, sesamoidectomy showed earlier return to play compared to internal fixation. Finally, athletes with fibular sesamoid injuries returned to their sport earlier than tibial sesamoid injuries.

Anderson and McBryde reported on 21 patients treated with bone grafting for symptomatic tibial sesamoid nonunions ( Fig. 11-19 ). They curetted and bone grafted the diastasis, which was typically 1-mm wide. All patients were noted to have a positive bone scan before surgery. In two cases in which articular surface deterioration was noted, a sesamoidectomy was performed. Three other patients had excessive motion at the diastasis site and were not considered candidates for bone grafting. Through an inferior extraarticular approach, they curetted and bone grafted the diastasis “nonunion site.” No internal fixation was used. The patients were placed in a below-knee cast and kept non–weight bearing for 4 weeks. At final follow-up, 19 of 21 sesamoids had healed. Two patients had a persistent nonunion.

Reports in which internal fixation has been used for acute sesamoid fracture or chronic nonunions have noted success. Riley and Selner used a cerclage wire and bone grafting in one case, and Blundell et al used a percutaneous screw in nine cases and reported successful union. Pagenstert et al reported two cases in which simultaneous correction of a hallux valgus deformity was combined with open reduction and internal fixation of a nonunion of a medial sesamoid.

Partial excision may be an option for asymmetric bipartite sesamoids. Rodeo et al reported on four cases of injuries to the hallux with progressive diastasis of bipartite sesamoids. The patients were treated with a distal resection of a smaller fragment and repair of the sesamoid mechanism. Biedert and Hintermann reported on five athletes who developed stress fractures of the medial sesamoids. Surgical excision of the proximal fragment and repair of the flexor hallucis brevis were performed. After casting for 6 weeks after surgery, full return to sports activity was allowed at 8 weeks.

Complete sesamoidectomy may be considered for irreparable sesamoids. Kuo et al reported a case of nonunion of the fibular sesamoid in association with chronic gout that required surgical excision. Brodsky et al retrospectively reviewed a series of 37 patients with fractured sesamoids. Avascular necrosis secondary to fracture was noted in 9 cases, 16 cases were diagnosed as stress fractures, and 12 cases were related to direct trauma. After surgical excision of the fractured sesamoid, an average postoperative American Orthopaedic Foot and Ankle Society (AOFAS) score of 93 was achieved. Saxena and Krisdakumtorn reported on 24 patients at a mean follow-up of 86 months after sesamoidectomy. There were 10 fibular and 16 tibial sesamoidectomies. Eleven patients were professional or varsity athletes and returned to activity in 7.5 weeks. The other patients returned to normal activities in 12 weeks. Complications included one varus deformity, one valgus deformity, and two cases of neuroma formation associated with fibular sesamoidectomy. Patients took longer to recover from surgery for tibial sesamoidectomy, which the authors surmised was probably due to increased weight bearing. Patients with fibular sesamoidectomies had an earlier return to activity. They noted that a dorsolateral approach may be more difficult for fibular sesamoidectomy and that the two nerve problems both occurred with a dorsolateral approach.

Congenital Absence of the Sesamoids

Congenital variations of the ossification of the tibial and fibular sesamoids are common. Congenital absence of a sesamoid has been infrequently reported; however, it is probably more prevalent than is realized. Patients are typically asymptomatic with absent sesamoids. Inge and Ferguson reported two cases of congenital absence of the tibial sesamoid. Goez and DeLauro, Zinsmeister and Edelman, and others have reported absence of the tibial sesamoids as well. Jeng et al and others have reported cases of an absent fibular sesamoid ( Fig. 11-20 ).

Although absence of a sesamoid can be asymptomatic, removal of a sesamoid for painful plantar keratosis can cause postoperative pain beneath the remaining sesamoid. The absence of a tibial sesamoid can produce a clawing of the hallux or development of a progressive postoperative hallux valgus deformity (see Fig. 11-20D ).

Jahss has reported that congenital absence of both sesamoids is extremely rare ( Fig. 11-21D and E ). Wright reported one case of bilateral absence of both sesamoids associated with hallux varus deformity, and Williams et al reported a case of bilateral congenital absence with associated metatarsalgia ( Fig. 11-21A–C ).

Distorted or Hypertrophied Sesamoids

Congenital variations of the sesamoids can lead to localized discomfort if the plantar surface of the sesamoid is irregular. Hypertrophy of a sesamoid can create an extraordinarily large or thickened projection on the plantar surface and lead to development of a hyperkeratotic lesion ( Fig. 11-22 ). Mowad et al described an osteochondroma of the tibial sesamoid manifesting with a painful plantar mass and a hypertrophic plantar keratosis ( Fig. 11-23A and B ).

Acquired irregularities of a sesamoid can result from a congenital anomaly in the shape of the sesamoid, from previous injury, or from a rotational deformity of the great toe. Although the sesamoids normally articulate with the plantar metatarsal facets (see Fig. 11-3 ), pronation of the hallux with adduction of the first metatarsal tends to lead to a rotational deformity in the metatarsal sesamoid articulation. This distortion can lead to hypertrophy of the sesamoid. If the hypertrophy occurs in a plantar direction, excess bone formation can lead to a symptomatic keratotic lesion that can ultimately ulcerate because of weight-bearing pressure.

Unrelenting pain with ambulation is the most common presenting symptom of a hypertrophied or distorted sesamoid. Although a thickened keratotic lesion may be mistaken for a verruca plantaris, trimming of the keratosis helps to differentiate the two lesions.

The soft tissue directly beneath the sesamoids can ulcerate, leading to secondary infection and osteomyelitis. A misshapen or hypertrophied fibular sesamoid is infrequently associated with a keratotic skin lesion because normally there is minimal weight bearing on the fibular sesamoid. Nonetheless, a patient can experience pain in the first intermetatarsal space because of local irritation ( Fig. 11-24A–C ), and occasionally, an exostosis develops on the fibular sesamoid (see Fig. 11-20D ). Saxby et al have reported that a case of coalition of the tibial and fibular sesamoids with plantar pain was treated successfully with a custom orthotic device used to relieve pressure beneath the symptomatic sesamoid coalition ( Fig. 11-25 ). Shaving of the symptomatic keratoses and the use of a metatarsal pad, scaphoid pad, or prefabricated or custom orthotic device can redistribute the weight-bearing pressures and relieve symptoms (see Fig. 11-18 ). With protracted symptoms, sesamoid plantar shaving or sesamoidectomy may be necessary.

Intractable Plantar Keratoses

An intractable plantar keratotic lesion can develop beneath the tibial sesamoid without significant hypertrophy or previous injury. Because of the position of the tibial sesamoid and its increased weight-bearing status, it is the tibial sesamoid that is often associated with an intractable plantar keratosis. A keratotic lesion can develop with a cavus foot deformity or with a plantarflexed first ray, and this anatomy must be considered when evaluating a keratosis beneath the first metatarsal head.

An osseous deformity of the sesamoid or malalignment of the foot can also lead to development of a symptomatic plantar keratotic lesion. A more diffuse keratosis beneath the entire metatarsal head is usually associated with a plantarflexed first ray or cavus deformity. A more localized callus is usually associated with a prominent sesamoid.

Keratotic lesion may be debrided or shaved to reduce their plantar prominence. A custom-molded orthosis or a soft pad placed just proximal to the symptomatic lesion often alleviates symptoms. An extra-depth shoe (increased vertical volume) with a prefabricated or custom insole can provide relief of symptoms (see Fig. 11-18D ).

With continued symptoms, plantar shaving of the sesamoid itself can alleviate symptoms without impairing joint function. Occasionally, a sesamoidectomy is necessary for an intractable lesion. Resection of a sesamoid in the presence of a cavus deformity or a plantar-flexed first ray is often associated with the recurrence of a plantar keratotic lesion. In this situation, a closing-wedge dorsiflexion metatarsal osteotomy is preferable ( Fig. 11-26 ).

Bursitis

Jahss estimates that a bursa exists under the first metatarsal in 30% of normal feet ( Fig. 11-27 ). With a cavus foot, a plantar-flexed metatarsal, or just excessive ambulation or standing, a subacute or chronic sesamoid bursitis can develop. Chronic bursitis may be associated with a hypertrophied or arthritic medial sesamoid as well. Kernohan et al reported a case of painful calcific bursitis of the sesamoid treated successfully with surgical debridement.

Redistribution of weight bearing with the use of a custom orthotic device or metatarsal pad placed just proximal to the symptomatic sesamoid often diminishes discomfort (see Fig. 11-18 ). When symptoms are refractory to conservative treatment, surgery should be tailored to the underlying cause. A bursectomy sometimes gives long-lasting relief when a plantarflexed first metatarsal or cavus foot is the underlying cause of symptoms. When the medial sesamoid is the cause of continued symptoms, surgical excision with resection of the overlying bursa often relieves symptoms.

Nerve Compression

The plantar-medial digital nerve and plantar-lateral digital nerve are located adjacent to the medial and lateral sesamoids ( Fig. 11-28 ). Impingement of either of these branches may be a source of pain in the area of the sesamoids. Helfet reported compression of the lateral plantar cutaneous nerve to the hallux. The plantar-medial digital nerve can also be compressed by the medial sesamoid in a similar fashion. Often, pain is difficult to differentiate from pain localized to the adjacent sesamoid. Occasionally, a Tinel sign can be detected at the site of nerve compression. Patients might or might not appreciate decreased sensation distal to the nerve compression.

A metatarsal pad or custom orthosis can relieve symptoms of a compressed nerve. Continued symptoms in spite of conservative care can necessitate surgical intervention. Surgical excision of the involved sesamoids may be used to relieve pain; however, a surgeon must isolate and protect the involved nerve to avoid injury. A postoperative neuroma after surgery may be more symptomatic than a patient’s original complaint.

Arthritis

Degenerative arthritis of the first metatarsal sesamoid articulation has been reported by several investigators. Subchondral cyst formation can develop as a secondary change. Symptoms may be associated with rheumatoid arthritis, hallux rigidus, psoriatic arthritis, or other systemic arthritides. Diffuse idiopathic skeletal hyperostosis (DISH) can involve the sesamoids and lead to osteophyte formation. Rupture of either the abductor hallucis or the adductor hallucis can result in the development of progressive hallux valgus or hallux varus. Complete rupture of the plantar plate can lead to clawing of the hallux.

Alternatively, localized degenerative arthritis of one or more of the sesamoids can occur. Scranton and Rutkowski reported erosion of articular cartilage in cases of progressive sesamoid chondromalacia that eventually required surgical excision. Degenerative arthritis of the metatarsal sesamoid articulation can develop as a progression of localized trauma, progressive hallux valgus, chondromalacia, rounded first metatarsal head, hallux rigidus, increased age, or sesamoiditis ( Fig. 11-29 ).

Initial symptoms include swelling, synovitis, and erythema and can be demonstrated on physical examination. Restricted MTP joint motion, pain with forced dorsiflexion, and pain on localized palpation may be noted as well.

Treatment

The goal of conservative care is to relieve discomfort with ambulation. A stiff insole, extended shank, rocker outer sole, and custom orthosis or metatarsal pad that relieves pressure beneath the first metatarsal head or reduces MTP joint motion often eliminates symptoms. Nonsteroidal antiinflammatory drugs (NSAIDs) can also decrease inflammation.

Surgical resection of the involved sesamoid may also be considered for isolated arthritis of either the lateral or medial sesamoid. In the presence of long-standing arthritis, MTP joint motion often fails to improve with surgical resection of a sesamoid, although pain may be significantly relieved. When both the medial and lateral sesamoids are involved, a combined resection may be contraindicated because it will destroy the intrinsic insertion of the flexor digitorum brevis and may lead to clawing of the great toe. Julsrud reported dual excision of the sesamoids with a combined hallux interphanlangeal joint fusion in the treatment of osteonecrosis of both sesamoids. Bouché has suggested that with careful excision of both sesamoids, the IP joint may not require an arthrodesis. Tagoe et al, however, have reported a series of 36 cases in which a dual sesamoid resection was performed. The authors reported satisfactory results when this was combined with a dorsal cheilectomy. They suggested that the reason for lack of progressive MTP or IP joint deformity postoperatively may have been related to the restricted MTP joint range of motion at the time of surgery. We suggest that an MTP joint arthrodesis may be the preferred alternative to both stabilize the joint and relieve pain. A Keller resection arthroplasty is another alternative, although it can lead to postoperative clawing of the hallux as well ( Fig. 11-30 ). Dual sesamoidectomy should be considered a salvage procedure and is performed uncommonly.

Subluxation and Dislocation of the Sesamoids

As the magnitude of a hallux valgus deformity increases, pronation of the great toe occurs. As the hallux migrates into valgus, the first metatarsal deviates medially. As the deformity increases, the first metatarsal head progressively subluxates off of the sesamoid mechanism. Although the term “sesamoid subluxation” is associated with a hallux valgus deformity, the sesamoid migration occurs solely in relation to the first metatarsal head. The sesamoid mechanism retains its relationship anatomically to the second metatarsal because it is tethered by the transverse metatarsal ligament and the conjoined adductor hallucis tendon. Increased weight-bearing forces are transmitted through the first metatarsal head and tibial sesamoid. The fibular sesamoid, however, becomes displaced into the first intermetatarsal space, where weight-bearing forces are diminished.

Weil and Hill, in an evaluation of 500 normal radiographs, noted a 15% incidence of bipartite tibial sesamoids in the general population. In contrast, in the examination of 500 radiographs of feet with hallux valgus, they observed a 32% incidence of hallux valgus associated with bipartite tibial sesamoids and concluded that multipartite sesamoids can predispose the first ray to a hallux valgus deformity.

As sesamoid displacement develops, the intersesamoid ridge erodes (see Fig. 11-3 ). There is quite often complete cartilage absence in the former location of the cristae ( Fig. 11-31 ). Axial radiographs often show gradual attrition of the intersesamoid ridge with a mild and moderate hallux valgus deformity. With a severe deformity, complete erosion of the crista occurs. Insertion of the conjoined adductor tendon into the plantar-lateral base of the proximal phalanx and lateral sesamoid leads to a pronation or rotational force on the great toe as the hallux valgus deformity increases. Moreover, as the subluxation and rotation worsen, there is increased stress to the area resulting in worsening arthritis at the sesamoid metatarsal articulation.

Treatment

After correction of a hallux valgus deformity, the alignment of the sesamoids may be undercorrected, adequately corrected, or overcorrected. Although the goal is to realign the sesamoids with the first metatarsal plantar facets, it may be necessary to achieve this correction through release of the conjoined adductor tendon and lateral capsular structures. On occasion, a lateral sesamoidectomy is performed. Although such procedures allow relocation of the tibial sesamoid to the plantar-medial facet of the first metatarsal, an unstable situation occasionally develops because of erosion of the intersesamoid ridge. In this case, the medial facet is no longer a stable articulating surface. Recurrent lateral sesamoid migration with the development of a recurrent hallux valgus deformity or medial migration of the tibial sesamoid with a resultant hallux varus deformity can occur ( Fig. 11-32 ). The use of semirigid dressings in the acute postoperative period can help to maintain the surgical correction until the sesamoid mechanism becomes stabilized.

Although McBride recommended excising the fibular sesamoid to achieve adequate release of the lateral capsular contracture, we believe a fibular sesamoid should rarely be removed in the correction of a hallux valgus deformity. After a complete lateral soft tissue release has been performed, if a significant contracture remains or if significant degenerative changes of the lateral sesamoid restrict adequate MTP joint motion with realignment of the hallux, a fibular sesamoid resection may be contemplated. An 8% incidence of postoperative hallux varus after a McBride procedure has been reported where a fibular sesamoid has been removed. A postoperative hallux varus deformity is associated with the correction of hallux valgus deformities of a more severe nature (hallux valgus angle greater than 40 degrees). Complete erosion of the intersesamoid ridge coupled with a contracted intrinsic musculature can lead to this potentially unstable situation. Overaggressive medial capsulorrhaphy and an excessive medial exostectomy can predispose to a postoperative hallux varus deformity.

Lee et al reported their results after 14 cases of isolated tibial sesamoidectomy. They performed a meticulous medial capsular repair and found no change in hallux valgus or 1- to 2 intermetatarsal angles or toe strength at an average of 62 months of follow-up.

Infection

Infections of the sesamoids are not common; however, several cases have been reported in the orthopaedic literature. Osteomyelitis of the sesamoid can develop after trauma, a puncture wound, or breakdown of the plantar skin with chronic neuropathic ulceration. Often, osteomyelitis of the sesamoid progresses to infection of the MTP joint. A gram-negative or multi-organism bacterial infection is often associated with chronic plantar ulceration.

On physical examination, the MTP joint becomes swollen and erythematous. Manipulation of the hallux causes pain. Careful sensory exam is performed because loss of sensation is a risk for skin breakdown and sesamoid infection. Hypertrophic callus formation beneath the sesamoids can develop because of increased pressure. Skin breakdown and trophic ulceration can develop with subsequent osteomyelitis. Often, a delay in diagnosis occurs because of the insidious nature of the infection. Radiographic changes can be very slow to develop.

Early conservative treatment prior to deep infection setting in may be used to reduce pressure beneath the sesamoids. A molded insole or metatarsal pad can reduce pressure beneath the sesamoids and paring of abundant callus can relieve symptoms (see Fig. 11-18 ). In the case of a diabetic patient who has an ulcer beneath the first metatarsal head, measures to ensure that the ulceration does not recur should be undertaken after the acute infection has subsided. Use of extra-depth shoes with a polyethylene foam (Plastizote) insert (see Fig. 11-18B2 ) can significantly reduce the recurrence of ulceration.

Where osteomyelitis of the sesamoid has developed, surgical excision may be necessary. In the case of acute infection, an attempt should be made to make a bacteriologic diagnosis at the time of the surgical debridement of the sesamoid. Excision of either or both sesamoids may be necessary, depending upon the extent of the infection. Irrigation, aggressive debridement, and localized wound care are often necessary to achieve control of the wound. Although a double sesamoidectomy should be routinely avoided, advanced osteomyelitis with involvement of both sesamoids can necessitate their removal ( Fig. 11-33 ). Preservation of the tendons of the abductor and adductor hallucis and subperiosteal resection of the sesamoids can help to prevent a cock-up deformity of the hallux. An interphalangeal arthrodesis might eventually be necessary after dual sesamoid excision to treat a clawing of the interphalangeal joint of the hallux. Postoperatively, restricted range of motion and decreased strength of the hallux are noted after sesamoidectomy; however, often the scarring that develops after infection prevents the claw toe deformity that typically develops after a bilateral sesamoid resection.

Osteonecrosis of the Sesamoids

Osteonecrosis of the sesamoids is a rare condition that can affect either sesamoid. It is characterized by pain, tenderness to palpation, and osseous fragmentation or mottling on radiographic examination. Ilfeld and Rosen described osteochondritis of the sesamoid and noted it occurred infrequently. Although the cause is unclear, Helal and Brodsky suggested that osteochondritis develops after trauma or a crush injury. Kliman et al hypothesized that the development of a sesamoid stress fracture and the subsequent reparative process led to osteochondritis.

Although trauma is likely to be the most common cause, Jahss has associated osteonecrosis with diminished vascularity. Other causes include nonunion, mechanical overload, or atraumatic avascular necrosis. He noted that osteonecrosis tends to occur in women around the age of 25 years, but it can occur in both sexes from 13 to 80 years of age. Jahss reports that the tibial and fibular sesamoids are equally involved. Julsrud reported simultaneous osteonecrosis in a 22-year-old woman.

The circulation of the sesamoids can play a role in the development of osteonecrosis. Rath et al and others (see Figs. 11-9 and 11-10 ) have described the arterial circulation of the sesamoids. Individual arterial patterns can predispose a sesamoid to degeneration after injury. An injury pattern that disrupts the interosseous circulation can predispose an injured sesamoid to osteonecrosis. Often, however, a patient gives no history of injury. On physical examination, pain and tenderness are localized to the involved sesamoid. The metatarsal head is usually nontender.

The diagnosis of osteonecrosis is usually made initially by an axial radiograph depicting the sesamoid in profile ( Fig. 11-34A–C ). Often, radiographic findings are negative for 9 to 12 months. In time, lysis and resorptive changes in the involved sesamoid are combined with areas of sclerosis. Mottling, fragmentation, flattening, and elongation of the sesamoid can develop. Historically, a high-resolution technetium bone scan was done to help make the diagnosis of osteochondritis in the absence of radiographic findings. With a bone scan, typically the sesamoid demonstrates increased uptake without significant involvement of the MTP joint ( Fig. 11-34D ).

An MRI can aid in the evaluation and diagnosis of osteonecrosis if radiographs do not show a clear pathology, especially early in the disease process. In the setting of a fragmented sesamoid, MRI can help delineate between a bipartite sesamoid, nonunion, or avascular necrosis. In addition, an MRI may show acute edema in the involved sesamoid that is commonly seen early in the disease process of AVN, and later, when fragmentation develops ( Figs. 11-35–11-37 ). Late-stage findings are associated with bone sclerosis and low signal on all pulse sequences and lack of contrast enhancement although contrast is typically not needed for evaluation of avascular necrosis. A computed tomography (CT) scan may better demonstrate bone sclerosis and late stage fragmentation more clearly than MRI.

Sesamoiditis

The diagnosis of sesamoiditis is a diagnosis of exclusion. Often, this condition occurs in teenagers and young adults and may be associated with trauma. Pain on weight bearing is a typical complaint. Often, there is tenderness to palpation over the involved sesamoid, which may be accompanied by inflammation or a bursal thickening on the plantar aspect of the sesamoid mechanism. The onset may be sudden or gradual, with pain on weight bearing and dorsiflexion of the great toe. Although radiographic findings are typically normal, a high-resolution technetium bone scan might demonstrate increased blood flow to the involved sesamoid.

Some types of trauma associated with sesamoid injuries include jumping from a height, excessive walking or dancing, excessive dorsiflexion of the MTP joint, or the chronic use of high-fashion footwear. The tibial sesamoid is more often involved because of increased weight bearing in this area of the first metatarsal head.

Dobas and Silvers defined sesamoiditis as an inflammation and swelling of the peritendinous structures involving the sesamoids. Apley referred to “chondromalacia of the sesamoids” and described a condition similar to sesamoiditis. Apley dissected the medial sesamoid and found remarkable similarities between the articular cartilage and the degeneration seen with sesamoiditis and that of chondromalacia of the patellofemoral joint. Hong et al observed degeneration of the hyaline cartilage in surgical specimens resected with intractable pain and a diagnosis of chondromalacia or sesamoiditis.

Decreased walking activities and the use of metatarsal pads and custom foot orthoses may reduce weight-bearing pressure and relieve symptoms. A stiff-soled shoe or a graphite insole can diminish MTP joint motion and relieve pain (see Fig. 11-16 ). Taping of the great toe in some degree of plantar flexion also helps to relieve pressure on the sesamoids ( Fig. 11-38 ). Decreasing shoe heel height can reduce pressure on the involved sesamoid and relieve symptoms. NSAIDs are also efficacious at times. In the presence of continuing symptoms, surgical excision may be necessary.

Physical Examination

Patients with a symptomatic sesamoid often complain of pain and discomfort during the toe-off phase of gait. Objective clinical findings include restricted range of MTP motion, pain on direct palpation, pain with motion of the first MTP joint, swelling of the first MTP joint, and diminished plantar or dorsiflexion strength. With careful palpation, the medial sesamoid may be distinguished from the lateral sesamoid. Synovitis of the first MTP joint may be noted as well on physical examination. Occasionally, an intractable plantar keratotic lesion develops beneath either the tibial or fibular sesamoid.

The orientation of the hallux must be inspected for lateral (hallux valgus) or medial (hallux varus) deviation or for clawing of the hallux. Progressive insidious deviation of the hallux can develop with sesamoid disruption caused by trauma or fracture. Progressive hallux valgus or hallux varus can also develop because of a previous sesamoid resection. Hyperextension of the hallux because of discontinuity of the sesamoid complex can occur after traumatic rupture of the plantar plate (see Fig. 11-8 ).

Examination of the sensory nerves of the first ray is important in diagnosing a compressed digital nerve, which can manifest with isolated neuritic symptoms or numbness. With compression of either the medial or lateral digital nerve by either the tibial or fibular sesamoid, a Tinel sign can be elicited along the border of the sesamoid.

Radiographic Examination

Routine dorsoplantar and lateral radiographs ( Fig. 11-39A and B ) can provide limited information in the evaluation of a painful sesamoid. On the dorsoplantar view, the metatarsal head overlies both the medial and lateral sesamoid and often obscures detail; on the lateral projection, the medial and lateral sesamoids overlap each other. The fibular sesamoid is best demonstrated in a lateral oblique radiograph ( Fig. 11-39C ), where it can be seen between the first and second metatarsal heads. The tibial sesamoid is best seen on a medial oblique radiograph ( Fig. 11-39D ). With the MTP joint dorsiflexed approximately 50 degrees, the roentgen beam is directed 15 degrees cephalad from a lateral position and is centered over the first metatarsal head. Often, the most useful radiograph is the axial sesamoid view ( Fig. 11-39E ). Historically, where radiographs appeared normal in spite of a patient’s subjective symptoms, a technetium-99m ( ^99m Tc) bone scan was done to evaluate the sesamoids ( Fig. 11-40 ). A bone scan can demonstrate increased uptake before the development of any significant radiographic change, such as sclerosis, fragmentation, or disintegration. However, magnetic resonance imaging (MRI) has supplanted bone scan for evaluation of the sesamoids. An MRI may demonstrate bone edema, avascular regions, fracture, fragmentation, or degeneration of a sesamoid before radiographic changes are demonstrated on plain radiographs (see Fig. 11-4A ). In addition, CT examination can define osseous changes, such as acute fracture or fragmentation.

Surgical Technique ( Video 11-1 )

• 1.

  A longitudinal plantar-medial incision is made similar to that used for a medial sesamoidectomy ( Fig. 11-43A ).

  

• 2.

  Care is taken to isolate the medial plantar digital nerve, which courses over the medial border of the tibial sesamoid ( Fig. 11-43B ).

• 3.

  The metatarsal sesamoid ligament is incised to define the superior extent of the sesamoid ( Fig. 11-43C ).

• 4.

  The plantar fat pad is retracted, and a sagittal saw is used to resect the plantar half of the sesamoid ( Fig. 11-44A and B ).

  

• 5.

  Care is taken to protect the flexor digitorum longus tendon, which lies immediately lateral to the tibial sesamoid.

• 6.

  Once the tibial sesamoid has been shaved, the sharp edges are beveled with a rongeur.

• 7.

  The skin is approximated in a routine fashion ( Fig. 11-43I ).

• 8.

  The toe is protected in a gauze-and-tape dressing, and the patient is allowed to ambulate in a postoperative shoe for 3 weeks after surgery.